docs: def remove_edge(self, u, v):
          """Version of remove_edge that's much like normal networkx but only
          deletes once, since the database doesn't keep separate adj and
          succ mappings
  
          """
          try:
              del self.succ[u][v]
          except KeyError:
              raise NetworkXError(
                  "The edge {}-{} is not in the graph.".format(u, v)
              )